全文获取类型
收费全文 | 570篇 |
免费 | 12篇 |
国内免费 | 111篇 |
专业分类
化学 | 582篇 |
晶体学 | 3篇 |
力学 | 5篇 |
综合类 | 1篇 |
数学 | 12篇 |
物理学 | 90篇 |
出版年
2024年 | 3篇 |
2023年 | 34篇 |
2022年 | 15篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 7篇 |
2013年 | 40篇 |
2012年 | 35篇 |
2011年 | 38篇 |
2010年 | 36篇 |
2009年 | 49篇 |
2008年 | 33篇 |
2007年 | 38篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 11篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有693条查询结果,搜索用时 31 毫秒
51.
G.M.N. Costa T. Dias M. Cardoso Y. Guerrieri F.L.P. Pessoa S.A.B. Vieira de Melo M. Embiruu 《Fluid Phase Equilibria》2008,267(2):140-149
A large number of equations of state and activity coefficient models capable of describing phase equilibria in polymer solutions are available today, but only a few of these models have been applied to different systems. It is therefore useful to investigate the performance of existing thermodynamic models for complex polymer solutions which have not yet been widely studied. The present work studies the application of several activity coefficient models [P.J. Flory, Principles of Polymer Chemistry, Cornell University Press, New York, NY, 1953; T. Oishi, J.M. Prausnitz, Estimation of solvent activities in polymer solutions using a group-contribution method, Ind. Eng. Chem. Process Design Dev. 17 (1978) 333; H.S. Elbro, A. Fredenslund, P. Rasmussen, A new simple equation for the prediction of solvent activities in polymer solutions, Macromolecules 23 (1990) 4707; G.M. Kontogeorgis, A. Fredenslund, D. Tassios, Simple activity coefficient model for the prediction of solvent activities in polymer solutions, Ind. Eng. Chem. Res. 32 (1993) 362; C. Chen, A segment-based local composition model for the Gibbs energy of polymer solutions, Fluid Phase Equilib. 83 (1993) 301; A. Vetere, Rules for predicting vapor–liquid equilibria of amorphous polymer solutions using a modified Flory–Huggins equation, Fluid Phase Equilib. 97 (1994) 43; C. Qian, S.J. Mumby, B.E. Eichinger, Phase diagrams of binary polymer solutions and blends, Macromolecules 24 (1991) 1655; Y.C. Bae, J.J. Shim, D.S. Soane, J.M. Prausnitz, Representation of vapor–liquid and liquid–liquid equilibria for binary systems containing polymers: applicability of an extended Flory–Huggins equation, J. Appl. Polym. Sci. 47 (1993) 1193; G. Bogdanic, J. Vidal, A segmental interaction model for liquid–liquid equilibrium calculations for polymer solutions, Fluid Phase Equilibria 173 (2000) 241] and activity coefficient from equations of state [F. Chen, A. Fredenslund, P. Rasmussen, Group-contribution Flory equation of state for vapor–liquid equilibria en mixtures with polymers, Ind. Eng. Chem. Res. 29 (1990) 875; M.S. High, R.P. Danner, Application of the group contribution lattice—fluids EOS to polymer solutions, AIChE J. 36 (1990) 1625]. The evaluation of these models was carried out both at infinite dilution and at finite concentrations and the results compared to experimental data. Furthermore, liquid–liquid equilibrium predictions for binary polymer solutions using six activity coefficient models are compared in this work. The parameters were estimated for all the models to achieve the best possible representation of the reported experimental equilibrium behavior. 相似文献
52.
53.
以甲苯二异氰酸酯(TDI)为单体,在水与丙酮混合溶剂中通过沉淀聚合一步法制备了富含胺基的聚脲多孔材料(PPU),通过扫描电镜和压汞法对其表面形貌和孔结构进行了表征.PPU经戊二醛(GA)活化后用于荧光假单胞菌脂肪酶(PFL)的固定,考察了GA活化过程中GA浓度对酶固定量及固定酶活性的影响.结果表明,PPU是一种粒子尺寸分布在30~50μm范围的形状不规则的多孔粒子,孔径在2 nm~100μm之间呈连续分布.在pH=8.0的缓冲溶液中用0.17 mol/L的GA对PPU进行改性,将改性后的PPU用于PFL的固定,当酶溶液浓度为2.56 mg/m L时,得到酶的最大固定量为95.2 mg/g,固定酶的活性为375 U/mg,相对活性为76%.将此固定酶作为催化剂,用于1-苯乙醇外消旋化合物的手性拆分,并与游离酶催化的结果相比较.结果表明,固定酶的反应活性和立体选择性都明显优于游离酶.通过沉淀聚合制备的聚脲多孔材料在酶固定及手性分子拆分方面具有应用前景. 相似文献
54.
Vapour–liquid equilibria and densities for the ternary system chloroform + tetrahydrofuran + cyclohexane and for the binary mixtures containing chloroform have been determined at 298.15 K. Vapour–liquid equilibrium data have been collected by head-space gas-chromatographic analysis of the vapour phase directly withdrawn from an equilibration apparatus. Density measurements have been carried out by means of a vibrating tube densimeter. Molar excess Gibbs energies GE and volumes VE, as well as activity coefficients and apparent molar volumes of the components, have been obtained from the measured quantities and discussed. The binary chloroform + tetrahydrofuran displays negative deviations from ideality, while chloroform + cyclohexane positive deviations, for both volume and Gibbs energy. The GE's and VE's for the ternary system are positive in the region rich in cyclohexane while negative in the region rich in chloroform + tetrahydrofuran. This indicates that hydrogen bonding between chloroform and tetrahydrofuran molecules produces negative values of GE and VE and strongly influences the behaviour of the ternary system. 相似文献
55.
56.
The infinite dilution activity coefficients of exactly athermal fluids were calculated by Monte Carlo simulation with hard-core models. The hard-core models used in this work were hard-sphere and hard-spherocylinder models. The Widom test particle method was adopted to calculate the residual chemical potentials of solutes in pure solvent and in pure solute solutions. The infinite dilution activity coefficients of solutes were obtained from the residual chemical potentials of solutes. The infinite dilution activity coefficients calculated by Monte Carlo simulation were compared with those of athermal terms in activity coefficient equations. Staverman–Guggenheim equation overestimates the activity coefficients. The deviations of activity coefficients increase with increasing the hard-core volume of solute. Flory–Huggins equation based on molar volume gives good results for the hard-spherocylinder systems. Elbro-FV equation gives good results for both the hard-sphere and hard-spherocylinder systems. 相似文献
57.
槲皮素(Qu)是一种天然的、具有抗氧化活性的黄酮类化合物。本研究通过优化合成条件,制备了配位比分别为1:1和1:2(Qu/Ge)的QuGe和QuGe2两种配合物,并采用紫外、红外、核磁共振、元素分析、高效液相色谱、电化学等方法对配合物的结构进行表征。结果表明,QuGe中的Ge(Ⅳ)结合在3'位和4'位羟基的氧原子上,而QuGe2除了结合3'位和4'位羟基的位点外,还结合了4位CO和3位羟基。利用Fenton反应与罗丹明B体系,研究了Qu及其配合物的抗氧化活性。结果表明,两种配合物的抗氧化活性均比单独的Qu配体明显增强,并探讨了配合物抗氧化活性的增强机制,对开发具有保健功能的新型锗化合物具有重要意义。 相似文献
58.
59.
60.